Hew communication station and method for communicating longer duration ofdm symbols using minimum bandwidth units having tone allocations

ABSTRACT

Embodiments of a communication station and method for communicating in a wireless network are generally described herein. In some embodiments, the communication station may be to communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique. The channel resources may comprise one or more minimum bandwidth units with each minimum band-width unit having a predetermined number of data subcarriers. The station may also configure the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols. The longer-duration OFDM symbols may have symbols duration that is either 2× or 4× the standard OFDM symbol duration.

PRIORITY CLAIMS

This application claims the benefit of priority to the following United States Provisional Patent Applications:

Ser. No. 61/906,059, filed Nov. 19, 2013,

Ser. No. 61/973,376, filed Apr. 1, 2014,

Ser. No. 61/976,951, filed Apr. 8, 2014,

Ser. No. 61/986,256, filed Apr. 30, 2014,

Ser. No. 61/986,250, filed Apr. 30, 2014,

Ser. No. 61/991,730, filed May 12, 2014,

Ser. No. 62/013,869, filed Jun. 18, 2014, and

Ser. No. 62/024,801, filed Jul. 15, 2014,

which are all incorporated herein by reference in their entireties.

TECHNICAL FIELD

Embodiments pertain to wireless networks. Some embodiments relate to wireless local area networks (WLANs) and Wi-Fi networks including networks operating in accordance with the IEEE 802.11 family of standards. Some embodiments relate to the High Efficiency WLAN Study Group (HEW SG) (named DensiFi) and referred to as the IEEE 802.11ax SG. Some embodiments relate to high-efficiency wireless or high-efficiency WLAN (HEW) communications.

BACKGROUND

Wireless communications has been evolving toward ever increasing data rates (e.g., from IEEE 802.11a/g to IEEE 802.11n to IEEE 802.11 ac). In high-density deployment situations, overall system efficiency may become more important than higher data rates. For example, in high-density hotspot and cellular offloading scenarios, many devices competing for the wireless medium may have low to moderate data rate requirements (with respect to the very high data rates of IEEE 802.11 ac). The frame structure used for conventional and legacy IEEE 802.11 communications including very-high throughput (VHT) communications may be less suitable for such high-density deployment situations. A recently-formed study group for Wi-Fi evolution referred to as the IEEE 802.11 HEW SG (i.e., IEEE 802.11ax) is addressing these high-density deployment scenarios.

One issue with HEW is defining an efficient communication structure that is able to reuse at least some 802.11 ac hardware, such as a block interleaver. Another issue with HEW is defining an efficient communication structure that suitable for use with longer OFDM symbol durations.

Thus, there are general needs for devices and methods that improve overall system efficiency in wireless networks, particularly for high-density deployment situations. There are also general needs for devices and methods suitable for HEW communications. There are also general needs for devices and methods suitable for HEW communications that can communicate in accordance with an efficient communication structure and that is able to reuse at least some conventional hardware. There are also general needs for devices and methods suitable for HEW communications that can communicate in accordance with an efficient communication structure for using OFDM symbols of a longer duration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a HEW network in accordance with some embodiments;

FIG. 2 is a physical-layer block diagram of an HEW communication station in accordance with some embodiments;

FIG. 3 illustrates an HEW device in accordance with some embodiments; and

FIG. 4 is a procedure for communicating using minimum bandwidth units in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims

Some embodiments disclosed herein provide systems and methods for tone allocation in a HEW network. In some embodiments a master station may allocates tones for HEW to provide a smallest orthogonal frequency division multiple access (OFDMA) bandwidth unit (i.e., a minimum bandwidth unit). In some embodiments, an HEW communication station may be configured to communicate longer-duration orthogonal-frequency division multiplexed (OFDM) symbols on channel resources that comprise one or more minimum bandwidth units. Each minimum bandwidth unit may have a predetermined bandwidth and the minimum bandwidth units may be configured in accordance with one of a plurality of subcarrier (i.e., tone) allocations for one of a plurality of interleaver configurations. In some embodiments, optimum subcarrier allocations and interleaver size combinations are provided for use with the OFDMA minimum bandwidth units for communication using longer-duration OFDM symbols. These embodiments are discussed in more detail below. Some embodiments disclosed herein are applicable to communications using longer-duration OFDM symbols (e.g., larger FFT sizes).

FIG. 1 illustrates a HEW network in accordance with some embodiments. HEW network 100 may include a master station (STA) 102, a plurality of HEW stations 104 (HEW devices), and a plurality of legacy stations 106 (legacy devices). The master station 102 may be arranged to communicate with the HEW stations 104 and the legacy stations 106 in accordance with one or more of the IEEE 802.11 standards. In accordance with some HEW embodiments, the master station 102 and may be arranged to contend for a wireless medium (e.g., during a contention period) to receive exclusive control of the medium for an HEW control period (i.e., a transmission opportunity (TXOP)). The master station 102 may, for example, transmit a master-sync or control transmission at the beginning of the HEW control period to indicate, among other things, which HEW stations 104 are scheduled for communication during the HEW control period. During the HEW control period, the scheduled HEW stations 104 may communicate with the master station 102 in accordance with a non-contention based multiple access technique. This is unlike conventional Wi-Fi communications in which devices communicate in accordance with a contention-based communication technique, rather than a non-contention based multiple access technique. During the HEW control period, the master station 102 may communicate with HEW stations 104 (e.g., using one or more HEW frames). During the HEW control period, legacy stations 106 may refrain from communicating. In some embodiments, the master-sync transmission may be referred to as a control and schedule transmission.

In some embodiments, the multiple-access technique used during the HEW control period may be a scheduled OFDMA technique, although this is not a requirement. In some embodiments, the multiple access technique may be a time-division multiple access (TDMA) technique or a frequency division multiple access (FDMA) technique which may be combined with OFDMA. In some embodiments, the multiple access technique may be a space-division multiple access (SDMA) technique including a multi-user (MU) multiple-input multiple-output (MIMO) (MU-MIMO) technique, which may be combined with OFDMA. These multiple-access techniques used during the HEW control period may be configured for uplink or downlink data communications.

The master station 102 may also communicate with legacy stations 106 in accordance with legacy IEEE 802.11 communication techniques (outside the control period). In some embodiments, the master station 102 may also be configurable communicate with the HEW stations 104 outside the HEW control period in accordance with legacy IEEE 802.11 communication techniques, although this is not a requirement.

In some embodiments, the HEW communications during the control period may be configurable to have bandwidths of one of 20 MHz, 40 MHz, or 80 MHz contiguous bandwidths or an 80+80 MHz (160 MHz) non-contiguous bandwidth. In some embodiments, a 320 MHz channel width may be used. In some embodiments, subchannel bandwidths less than 20 MHz may also be used. In these embodiments, each channel or subchannel of an HEW communication may be configured for transmitting a number of spatial streams. HEW communications during the control period may be uplink or downlink communications.

In accordance with embodiments, an HEW station (e.g., master station 102 or an HEW station 104) may be configured to communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an OFDMA technique. The channel resources may comprise one or more minimum bandwidth units and each minimum bandwidth unit may have a predetermined number of data subcarriers. The longer-duration OFDM symbols may have symbol duration that is either 2× or 4× a standard OFDM symbol duration (i.e., the symbol time (e.g., T_(symbol))). The minimum bandwidth units may be configured in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations. These embodiments are discussed in more detail below. Some of the embodiments disclosed herein may be applicable to IEEE 802.11ax and HEW networks operating with a longer OFDM symbol duration (e.g., twice (2×) and four times (4×) the standard symbol duration).

As discussed in more detail below, an HEW station may comprise physical layer (PHY) and medium access control (MAC) layer circuitry. In some embodiments, the PHY circuitry may include a block interleaver having a depth of one OFDM symbol. The block interleaver may be configurable to interleave a block of encoded data in accordance with any one of the plurality of interleaver configurations. The interleaver configurations may comprise a number of columns and a number of rows.

FIG. 2 is a physical-layer block diagram of an HEW communication station in accordance with some embodiments. The PHY layer circuitry 200 may be suitable for use as a portion of the physical layer of an HEW communication station, such as master station 102 (FIG. 1) and/or HEW communication station 104 (FIG. 1). As illustrated in FIG. 2, the PHY layer circuitry 200 may include, among other things, one or more encoders 208, one or more block interleavers 214 and one or more constellation mappers 216. Each of the encoders 208 may be configured to encode input data prior to interleaving by the interleavers 214. Each of the constellation mappers 216 may be configured to map interleaved data to a constellation (e.g., a QAM constellation) after interleaving. Each interleaver 214 may be configured to interleave a block of encoded data in accordance with any one of the plurality of interleaver configurations. In some embodiments, the encoders 208 may be binary convolutional code (BCC) encoders. An FFT may be performed on the constellation-mapped symbols provided by the constellation mappers to generate time-domain signals for transmission.

In accordance with embodiments, the encoders 208 and mappers 216 operate in accordance with one of a plurality of predetermined modulation and coding scheme (MCS) combinations for the particular subcarrier allocation (i.e., the tone allocation). The plurality of predetermined MCS combinations for the subcarrier allocation may be restricted to an integer number of coded bits per OFDM symbol (Ncbps) and an integer number of data bits per OFDM symbol (Ndbps). In these embodiments, the number of coded bits per OFDM symbol (Ncbps) is an integer number and number of data bits per OFDM symbol (Ndbps) is an integer number. The predetermined MCS combinations and subcarrier allocations that may be used may include modulation orders of BPSK, QPSK, 16-QAM, 64-QAM and 256-QAM and coding rates of 1/2, 3/4, 2/3 and 5/6 provided that both the Ncbps and the Ndbps are integers. A non-integer Ndbps may result in a non-integer number of padding bits or the number of encoded bits exceeding the number of OFDM symbols which may lead to a minimum of one additional OFDM symbol comprised of only padding bits. An integer Ndbps may guarantee that all data lengths work with no additional padding using the 1 ln “Number of OFDM Symbols”, equation (20-32) in 802.11 2012 spec. Thus, embodiments disclosed herein may be restricted certain MCS combinations and subcarrier allocations. In these embodiments, the interleaver hardware architecture configurations are within the boundaries of an IEEE 802.11 interleaver allowing reuse of the legacy 802.11 hardware blocks for HEW.

In these embodiments, prior to interleaving, the communication station is configured to encode the input data based on a coding rate and subsequent to the interleaving, the communication station may be configured to constellation map interleaved bits to QAM constellation points based on a modulation level. The coding rate and modulation level may be in accordance with one of the predetermined MCS combinations for the particular subcarrier allocation. These embodiments are described in more detail below.

In some embodiments, each minimum bandwidth unit may be configurable for communication of between one and four spatial streams. In these embodiments, an SDMA or MIMO technique may be used during the control period to communicate the spatial streams.

Embodiments disclosed herein provide a number of data subcarriers, number of pilot subcarriers, and the size of block interleaver for the case of binary convolutional code (BCC) coding. In some embodiments, the structure of the OFDMA waveform for 802.1 lax described in United States Provisional Patent Application, Ser. No. 61/976,951, may be suitable for use, although this is not a requirement. Some embodiments disclosed herein describe the minimum bandwidth unit for the OFDMA waveform and describe an architecture of the subcarrier allocation. In some embodiments, the subcarrier allocation may be configured to reuse the IEEE 802.11 ac hardware to create the new OFDMA structure.

As outlined above, various embodiments disclosed herein provide a design of a smallest OFDMA bandwidth unit suitable for IEEE 802.11 ax configured networks operating with longer symbol duration (e.g., 2×, 4× of the 1 ln/ac OFDM symbol duration) (e.g., larger FFT sizes). These embodiments provide a number of data subcarriers, number of pilot subcarriers, and the size of block interleaver for the case of BCC coding. Disclosed herein are the possible allocations that are consistent with the IEEE 802.11ac interleave configurations. Some of the more preferable allocations may provide reduced overhead and ease of implementation, particularly when reuse of the IEEE 802.11 ac architecture is considered.

The longer symbol duration may be of particular interest for use in an outdoor environment where a more efficient cyclic prefix (CP) can be used to overcome the longer delay spread. Other benefits may include reduced CP overhead and a more relaxed clock timing accuracy than in an indoor environment.

The better configurations for the block interleaver may be based on the channel model, the MCS and other parameters, and may be determined by system simulation. Since the intent of the embodiments disclosed herein is to define subcarrier allocations, an exhaustive search within boundaries was performed to arrive at the reasonable subcarrier allocations.

Embodiments disclosed here provide for reuse, to a large extent, existing system parameters and system blocks. This makes the evolution less complicated and smaller through the reuse of existing system blocks and thus hardware, and thus less expensive. Therefore, the embodiments disclosed herein provide for reuse of the currently defined interleaver structure (with extensions for the narrower bandwidth), current code rates (with the ability to modify the rate) and modulation types (with the ability to modify the modulation size).

In an OFDMA system, the total number of subcarriers used in the smallest bandwidth unit may be a system design parameter. From this total subcarrier count, the OFDMA system has subcarriers that are assigned to data (used for data), pilot (typically used for time/frequency and channel tracking), guard (used to conform to a spectral mask) and the subcarriers at DC and around DC (to simplify direct conversion (DC) receiver designs). For example, in 20 MHz 802.11ac, the fixed subcarrier spacing is 312.5 kHz and thus the total number of subcarriers is 64. Of these 64 subcarriers, 52 are used for data, 1 for DC (i.e., nulled), 4 for pilot and the remaining 7 are used for guard (i.e., nulled).

Embodiments disclosed herein provide subcarrier allocations based on the set of modulation types used in previous systems (i.e., BPSK, QPSK, 16-QAM, 64 QAM and 256 QAM). The code rates (r) utilized in previous systems include the following set r=1/2, 3/4, 2/3 and 5/6. This set is not used for all modulation types in previous systems, but this does include all current rates used over the entire modulation set. To determine the valid subcarrier allocations, the same modulation and coding assignments may be used as done in the previous systems (e.g., IEEE 802.11a/.11n/.11ac). As outlined above, the embodiments disclosed herein may utilize the existing channel interleaver used in previous 802.11 systems. The channel interleaver is defined in section 22.3.10.8 of the IEEE Std. 802.11ac-2013, “IEEE Standard for Information Technology-Telecommunications and information exchange between systems—Local and metropolitan area networks—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz”. In that text, the interleaver parameters are outline in Table 22-17 “Number of Rows and columns in the interleaver”. The table is provided here for completeness for the case of 1 to 4 spatial streams.

TABLE 22-17 Number of rows and columns in the interleaver Parameter 20 MHz 40 MHz 80 MHz Ncol 13 18 26 Nrow 4 × N_(BPSCS) 6 × N_(BPSCS) 9 × N_(BPSCS) Nrot 11 29 58

In IEEE 802.11n, the introduction of a 40 MHz bandwidth channel reused the existing interleaver algorithm with modifications to the matrix size defined to write and read the data. In IEEE 802.11 ac, with the introduction of an 80 MHz bandwidth channel, the same interleaver algorithm was utilized. These parameters define the number of coded symbols that are stored in the interleaver. Some embodiments disclosed herein may also reuse the existing interleaver algorithm with new values to define N_(COL) and N_(ROW) for a minimum bandwidth unit. The N_(ROT) operation defines a rotation of the values when more than one spatial stream exists but does not define the interleaver size and thus will not affect the subcarrier allocation.

As can be seen in the table above, the N_(ROW) is a constant times the number of coded bits per subcarrier per stream. Thus, the interleaver physical size is a function of the MCS. Embodiments disclosed herein may define the constant (y), used in computing N_(ROW).

Using the above constraints a set of subcarrier allocations can be attained. As mentioned above, some of these embodiments are applicable to the longer symbol duration for the minimum bandwidth unit that allow multiplexing of up to four users within a 20 MHz channel bandwidth. These embodiments may be expandable to multiplexing of more than four users by dividing the allocations evenly to smaller allocations. For example, if multiplexing of eight users is of interest then the tone count found for that case of four users can be divided in each allocation evenly among two users to provide tone count for 2× of four users assuming that tone count is divisible by two. If however, the tone count is not divisible by 2 but it is divisible by 3, then multiplexing of 3× of four users will be possible.

As mentioned above in 20 MHz 802.11ac, the fixed (i.e., standard)* subcarrier spacing is 312.5 kHz and thus the total number of subcarrier is 64. Of these 64, 52 are used for data, 1 for DC (assumed nulled), 4 for pilot and the remaining 7 are used for guard (assumed nulled). In accordance with embodiments, for a 2× and a 4× symbol duration, the FFT sizes may be 128 and 256, respectively. Embodiments disclosed herein may provide from 24 to 32 subcarriers for each of four users for the data subcarriers, which would then allow 4 to 0 null subcarriers respectively for 4 users for 128-point FFT, and may provide from 48 to 64 subcarriers for each of four users for the data subcarriers, which would then allow 16 to 0 null subcarriers respectively for 4 users for 256-point FFT. To determine if a configuration is suitable for use, a set of equations may be used based on the following set of variables defined below:

N_(SD) Number of Data subcarriers N_(CBPS) Number of coded bits per symbol N_(BPSCS) Number of coded bits per single carrier N_(DBPS) Number of data bits per symbol N_(ROW) Interleaver Row size, equal to y * N_(BPSCS) r code rate M Modulation order (1 = BPSK, 2 = QPSK, 4 = 16-QAM, 6 = 64 QAM, 8= 256-QAM and 10 = 1024-QAM With those definitions the set of procedures and equations to determine if a configuration is valid is outlined below: 1. Select the number of Data subcarriers to test (N_(SD) ) 2. Compute N_(CBPS) = N_(SD) * M 3. Compute N_(BPSCS) = N_(CBPS) * N_(SD) 4. Compute N_(ROW) = y * N_(BPSCS); (where y is the assigned interleaver parameter) 5. Compute INT_(DIM) = N_(ROW) * N_(COL) ${6.\mspace{11mu} {Compute}\mspace{14mu} Z} = \frac{N_{CBPS}}{{INT}_{DIM}}$ 7. Compute M₁ = Z − └Z┘ 5. Compute M₂ = N_(DBPS) − └N_(DBPS)┘ 9. Test if ((M₁ = 0) & (M₂ = 0)) Then Valid, else not Thus if M₁ & M₂ = 0, then configuration using this code rate and modulation is allowable, otherwise disallowed.

Assuming that all modulations can be supported as in IEEE 802.11ac for 40MHz including 64QAM and 256QAM (introduced in 802.11ac) with code rates of 3/4 and 5/6, the suitable allocations allowed for a 256-point FFT are shown in Table 1 below and may include:

TABLE I NRow NCol Nsd 2 2 48 3 2 48 4 2 48 6 2 48 8 2 48 12 2 48 24 2 48 2 3 48 4 3 48 8 3 48 16 3 48 2 4 48 3 4 48 4 4 48 6 4 48 12 4 48 2 6 48 4 6 48 8 6 48 2 8 48 3 8 48 6 8 48 2 12 48 4 12 48 3 16 48 2 24 48 3 2 54 9 2 54 27 2 54 2 3 54 3 3 54 6 3 54 9 3 54 18 3 54 3 6 54 9 6 54 2 9 54 3 9 54 6 9 54 3 18 54 2 27 54 2 2 60 3 2 60 5 2 60 6 2 60 10 2 60 15 2 60 30 2 60 2 3 60 4 3 60 5 3 60 10 3 60 20 3 60 3 4 60 5 4 60 15 4 60 2 5 60 3 5 60 4 5 60 6 5 60 12 5 60 2 6 60 5 6 60 10 6 60 2 10 60 3 10 60 6 10 60 5 12 60 2 15 60 4 15 60 3 20 60 2 30 60

Table I shows three possibilities for the number of data tones: 48, 54 and 60 that would leave total of 64, 40, and 16 extra subcarriers within the 20 MHz. These extra subcarriers may be used for pilot tones per each subchannels, null at DC, and null subcarriers as guard bands, for example in a 20 MHz channel 54 data subcarriers, and 3 pilot tones can be assigned to each of four users plus three nulls at DC and 13 nulls on the left guard and 12 nulls on the right guard for the total of 4×(54+3)+3+13+12=256 subcarriers. This example allocation is within the current interleaver and supports all MCSs that result with several interleaver dimensions to select from. Among choices for interleaver dimensions, a closer to a square shape may be preferred (e.g., N_(COL)=6, and N_(ROW)=9), although other interleaver dimensions are also suitable.

In these embodiments, the master station 102 may be configured to process the longer-duration OFDM symbols with a fast-Fourier Transform (FFT). For processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit may be limited to one of 48, 54 and 60 data subcarriers. The interleaver configurations for these embodiments are shown in Table I.

The suitable allocations allowed for a 128-point FFT are shown in Table II below are:

TABLE II NRow NCol Nsd NRow NCol Nsd 2 2 24 3 2 30 3 2 24 5 2 30 4 2 24 15 2 30 6 2 24 2 3 30 12 2 24 5 3 30 2 3 24 10 3 30 4 3 24 2 5 30 8 3 24 3 5 30 2 4 24 6 5 30 3 4 24 5 6 30 6 4 24 3 10 30 2 6 24 2 15 30 4 6 24 3 8 24 2 12 24

In these embodiments, for processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 28 and 30 data subcarriers. The interleaver configurations for these embodiments are shown in Table II.

The suitable allocations for a 256-point FFT without support of code rate 5/6 with 256 QAM are shown in Table III below (e.g., the exclusion that is used for 20MHz in 802.11ac):

TABLE III NRow NCol Nsd 2 2 48 3 2 48 4 2 48 6 2 48 8 2 48 12 2 48 24 2 48 2 3 48 4 3 48 8 3 48 16 3 48 2 4 48 3 4 48 4 4 48 6 4 48 12 4 48 2 6 48 4 6 48 8 6 48 2 8 48 3 8 48 6 8 48 2 12 48 4 12 48 3 16 48 2 24 48 5 2 50 25 2 50 2 5 50 5 5 50 10 5 50 5 10 50 2 25 50 2 2 52 13 2 52 26 2 52 13 4 52 2 13 52 4 13 52 2 26 52 3 2 54 9 2 54 27 2 54 2 3 54 3 3 54 6 3 54 9 3 54 18 3 54 3 6 54 9 6 54 2 9 54 3 9 54 6 9 54 3 18 54 2 27 54 2 2 56 4 2 56 7 2 56 14 2 56 28 2 56 2 4 56 7 4 56 14 4 56 2 7 56 4 7 56 8 7 56 7 8 56 2 14 56 4 14 56 2 28 56 29 2 58 2 29 58 2 2 60 3 2 60 5 2 60 6 2 60 10 2 60 15 2 60 30 2 60 2 3 60 4 3 60 5 3 60 10 3 60 20 3 60 3 4 60 5 4 60 15 4 60 2 5 60 3 5 60 4 5 60 6 5 60 12 5 60 2 6 60 5 6 60 10 6 60 2 10 60 3 10 60 6 10 60 5 12 60 2 15 60 4 15 60 3 20 60 2 30 60 31 2 62 2 31 62

In these embodiments, for processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 48, 50, 54, 52, 54, 56, 60 and 62 data subcarriers. The interleaver configurations for these embodiments are shown in Table III.

The suitable allocations for a 128-point FFT without support of code rate 5/6 with 256 QAM are shown in Table IV below (e.g., the exclusion that is used for 20MHz in 802.11 ac):

TABLE IV NRow NCol Nsd NRow NCol Nsd 2 2 24 2 2 28 3 2 24 7 2 28 4 2 24 14 2 28 6 2 24 7 4 28 12 2 24 2 7 28 2 3 24 4 7 28 4 3 24 2 14 28 8 3 24 3 2 30 2 4 24 5 2 30 3 4 24 15 2 30 6 4 24 2 3 30 2 6 24 5 3 30 4 6 24 10 3 30 3 8 24 2 5 30 2 12 24 3 5 30 13 2 26 6 5 30 2 13 26 5 6 30 3 10 30 2 15 30

In these embodiments, for processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 24, 26, 28 and 30 data subcarriers. The interleaver configurations for these embodiments are shown in Table IV.

In some embodiments, the master station 102 may be configured to concurrently communicate using up to four of the minimum bandwidth units over channels of 20 MHz or 40 MHz during a control period in accordance with the OFDMA technique. In these embodiments when communicating using four minimum bandwidth units over a channel bandwidth, the master station 102 may communicate concurrently with up to four HEW stations 104 during the control period in accordance with an OFDMA technique. In these embodiments, when a 2× longer symbol duration is used in a 20 MHz channel bandwidth, for example, the subcarrier spacing may be reduced by a factor of two (e.g., half of 312.5 KHz), when a 4× longer symbol duration is used in a 20 MHz channel bandwidth, the subcarrier spacing may be reduced by a factor of four. In these embodiments, a subcarrier allocation with more guard subcarriers may be used for closer subcarrier spacing. In some embodiments, the station 102 may be configured to concurrently communicate using up to four of the minimum bandwidth units of each 20 MHz portion of a 40 MHz channel, an 80MHz channel and a 160 MHz channel.

In some embodiments, for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, one example of a subcarrier allocation comprises 256 total subcarriers including: 54 data subcarriers and 3 pilot subcarriers for each of the four minimum bandwidth units used for communicating within either channels of 20 MHz or 40 MHz, 2-4 null-subcarriers at DC, and 12-13 guard subcarriers at each band edge. For this example subcarrier allocation, the interleaver configurations shown in Table I may be suitable and support all current MCS configuration (i.e., without any code-rate restrictions).

In some embodiments, for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, one example of a subcarrier allocation that comprises 256 total subcarriers may include 54 data subcarriers and 3 pilot subcarriers for each of the four minimum bandwidth units used for communicating within either 20 MHz or 40 MHz channel bandwidth, 3 null-subcarriers at DC, 12 guard subcarriers at one band edge, and 13 guard subcarriers at the other band edge (e.g., the left and right side), for a total of 256 subcarriers (i.e., 4×(54+3)+3+12+13=256. For this example subcarrier allocation, the interleaver configurations shown in Table I may be suitable and support all current MCS configuration (i.e., without any code-rate restrictions). Other subcarrier allocations may also be suitable for use.

In some embodiments, the block interleaver 214 may have a depth of one OFDM symbol and may be configurable to interleave a block of encoded data. The interleaver configurations may comprise a number of columns (NCol) and a number of rows (Nrow) and the number of rows may be based on a number of coded bits per subcarrier per stream (N_(BPSCS)).

In some embodiments, for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, an example interleaver configuration has 9 columns and a number of rows (Nrow) equaling 3 times a number of coded bits per single subcarrier (N_(BPSCS)) (i.e., a 9×3 interleaver configuration). In these embodiments, the number of subcarriers (Nsd) times the modulation order (1-BPSK, 2-QPSK, etc.) is the number coded bits per symbol. The number of coded bits per single carrier may be computed by multiplying by the number of streams which then sets the interleaver size (N_(ROW)*N_(COL)) where N_(ROW) is the y*N_(BPSCS).

In some embodiments, the longer-duration OFDM symbols may be selected for larger delay spread environments (e.g., outdoors), and standard-duration OFDM symbols may be selected for smaller delay-spread environments (e.g., indoors). In these embodiments, a more efficient cyclic-prefix (CP) may be used to overcome the larger delay spread and may provide other benefits such as reduced CP overhead and relaxed clock-timing accuracy, among other things. The standard-duration OFDM symbols may have a symbol duration that ranges from 3.6 micro-seconds (us) including a 400 nanosecond (ns) short guard interval (e.g., for a 40 MHz channel) to 4 us including an 800 ns guard interval (e.g., for a 20 MHz channel). The longer-duration OFDM symbols may have a symbol duration is one of either 2× or 4× the duration of the standard-duration OFDM symbols.

FIG. 3 illustrates an HEW device in accordance with some embodiments. HEW device 300 may be an HEW compliant device that may be arranged to communicate with one or more other HEW devices, such as HEW stations and/or a master station, as well as communicate with legacy devices. HEW device 300 may be suitable for operating as master station or an HEW station. In accordance with embodiments, HEW device 300 may include, among other things, physical layer (PHY) circuitry 302 and medium-access control layer circuitry (MAC) 304. PHY 302 and MAC 304 may be HEW compliant layers and may also be compliant with one or more legacy IEEE 802.11 standards. PHY 302 may be arranged to transmit HEW frames. HEW device 300 may also include other processing circuitry 306 and memory 308 configured to perform the various operations described herein.

In accordance with some embodiments, the MAC 304 may be arranged to contend for a wireless medium during a contention period to receive control of the medium for the HEW control period and configure an HEW frame. The PHY 302 may be arranged to transmit the HEW frame as discussed above. The PHY 302 may also be arranged to receive an HEW frame from HEW stations. MAC 304 may also be arranged to perform transmitting and receiving operations through the PHY 302. The PHY 302 may include circuitry for modulation/demodulation, upconversion and/or downconversion, filtering, amplification, etc. In some embodiments, the processing circuitry 306 may include one or more processors. In some embodiments, two or more antennas may be coupled to the physical layer circuitry arranged for sending and receiving signals including transmission of the HEW frame. The memory 308 may be store information for configuring the processing circuitry 306 to perform operations for configuring and transmitting HEW frames and performing the various operations described herein.

In some embodiments, the HEW device 300 may be configured to communicate using OFDM communication signals over a multicarrier communication channel. In some embodiments, HEW device 300 may be configured to receive signals in accordance with specific communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) standards including IEEE 802.11-2012, 802.11n-2009 and/or 802.11ac-2013 standards and/or proposed specifications for WLANs including proposed HEW standards, although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. In some other embodiments, HEW device 300 may be configured to receive signals that were transmitted using one or more other modulation techniques such as spread spectrum modulation (e.g., direct sequence code division multiple access (DS-CDMA) and/or frequency hopping code division multiple access (FH-CDMA)), time-division multiplexing (TDM) modulation, and/or frequency-division multiplexing (FDM) modulation, although the scope of the embodiments is not limited in this respect.

In some embodiments, HEW device 300 may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone or smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. In some embodiments, HEW device 300 may include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, speakers, and other mobile device elements. The display may be an LCD screen including a touch screen.

The antennas 301 of HEW device 300 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some multiple-input multiple-output (MIMO) embodiments, the antennas 301 may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas and the antennas of a transmitting station.

Although HEW device 300 is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements of HEW device 300 may refer to one or more processes operating on one or more processing elements.

Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device.

FIG. 4 is a procedure for communicating longer-duration OFDM symbols using minimum bandwidth units in accordance with some embodiments. Procedure 400 may be performed by an HEW device, such as HEW station 104 or an HEW master device or station 102.

Operation 402 comprises configuring a block interleaver to interleave blocks of encoded input data in accordance with one of a plurality interleaver configurations determined for a subcarrier allocation of a minimum bandwidth unit for longer-duration OFDM symbols.

Operation 404 comprises processing symbols with either a 128-point FFT or a 256-point FFT to generate time-domain OFDMA waveforms. For processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit may be limited to one of 48, 54 and 60 data subcarriers. For processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 28 and 30 data subcarriers. For processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 48, 50, 54, 52, 54, 56, 60 and 62 data subcarriers. For processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit may be limited to one of 24, 26, 28 and 30 data subcarriers

Operation 406 comprises communicating the longer-duration OFDM symbols (in the form of the time-domain OFDMA waveforms) on channel resources comprising one or more minimum bandwidth units in accordance with non-contention based communication technique. In some embodiments, the longer-duration OFDM symbols may be communicated during a control period (e.g., a TXOP) in accordance with MU-MIMO technique.

In an example, a high-efficiency WLAN (HEW) communication station (STA) comprising physical layer and medium access control layer circuitry is configured to: communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configure the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols. The longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.

In another example, the station is configured to process the longer-duration OFDM symbols with a fast-Fourier Transform (FFT). For processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit is to be of 48, 54 or 60 data subcarriers. For processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit is to be of 28 or 30 data subcarriers. For processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 48, 50, 54, 52, 54, 56, 60 or 62 data subcarriers. For processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 24, 26, 28 or 30 data subcarriers.

In another example, the station is further configured to concurrently communicate using up to four of the minimum bandwidth units over channels of 20 MHz or 40 MHz during a control period in accordance with the OFDMA technique.

In another example, for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, the subcarrier allocation comprises 256 total subcarriers including: 54 data subcarriers and 3 pilot subcarriers for each of the four minimum bandwidth units used for communicating within either channels of 20 MHz or 40 MHz, 2-4 null-subcarriers at DC, and 12-13 guard subcarriers at each band edge.

In another example, the PHY circuitry includes a block interleaver having a depth of one OFDM symbol. The block interleaver may be configurable to interleave a block of encoded data, and the interleaver configurations may comprise a number of columns and a number of rows, the number of rows based on a number of coded bits per subcarrier per stream.

In another example, for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, the interleaver configuration has 9 columns and a number of rows equaling 3 times a number of coded bits per single subcarrier.

In another example, the communication station further comprises: an encoder configured to encode input data prior to interleaving in accordance with one of a plurality of code rates; and a constellation mapper to map the encoded data after the interleaving to a QAM constellation. The encoder and mapper operate in accordance with one of a plurality of predetermined modulation and coding scheme (MCS) combinations for the subcarrier allocation. The plurality of predetermined MCS combinations for the subcarrier allocation are restricted to an integer number of coded bits per OFDM symbol (Ncbps) and an integer number of data bits per OFDM symbol (Ndbps).

In another example, the longer-duration OFDM symbols are to be selected for larger delay spread environments, and standard-duration OFDM symbols are to be selected for smaller delay-spread environments.

In another example, the standard-duration OFDM symbols have a symbol duration that ranges from 3.6 micro-seconds (us) including a 400 nanosecond (ns) short guard interval to 4 us including an 800 ns guard interval, and the longer-duration OFDM symbols have a symbol duration is one of either 2× or 4× the duration of the standard-duration OFDM symbols.

In another example, the communication station further comprises one or more processors and memory, and the physical layer circuitry includes a transceiver.

In another example, the communication station further comprises two antennas coupled to the transceiver.

In another example, a method performed by a high-efficiency WLAN (HEW) communication station (STA) comprises: communicating longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configuring the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols. The longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.

In another example, the method further comprises processing the longer-duration OFDM symbols with a fast-Fourier Transform (FFT). For processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit is to be of 48, 54 or 60 data subcarriers. For processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit is to be of 28 or 30 data subcarriers.

In another example, for processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 48, 50, 54, 52, 54, 56, 60 or 62 data subcarriers, and for processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 24, 26, 28 or 30 data subcarriers.

In another example, the method comprises selecting the longer-duration OFDM symbols for larger delay spread environments, and selecting the standard-duration OFDM symbols for smaller delay-spread environments.

In another example, a non-transitory computer-readable storage medium stores instructions for execution by one or more processors to perform operations to configure a high-efficiency WLAN (HEW) communication station (STA) to: communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configure the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols. The longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment. 

1-20. (canceled)
 21. A high-efficiency WLAN (HEW) communication station (STA) comprising physical layer and medium access control layer circuitry to: communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configure the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols, wherein the longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.
 22. The communication station of claim 21 wherein the station is to process the longer-duration OFDM symbols with a fast-Fourier Transform (FFT), wherein for processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit is to be of 48, 54 or 60 data subcarriers, and wherein for processing the longer-duration (ADM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit is to be of 28 or 30 data subcarriers.
 23. The communication of station of claim 22, wherein for processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 48, 50, 54, 57, 54, 56, 60 or 62 data subcarriers, and wherein for processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 24, 26, 28 or 30 data subcarriers.
 24. The communication station of claim 23 wherein the station is further to concurrently communicate using up to four of the minimum bandwidth units over channels of 20 MHz or 40 MHz during a control period in accordance with the OFDMA technique.
 25. The communication station of claim 24, wherein for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, the subcarrier allocation comprises 256 total subcarriers including: 54 data subcarriers and 3 pilot subcarriers for each of the four minimum bandwidth units used for communicating within either channels of 20 MHz or 40 MHz, 2-4 null-subcarriers at DC, and 12-13 guard subcarriers at each band edge.
 26. The communication station of claim 24 wherein the physical-layer circuitry includes a block interleaver having a depth of one OFDM symbol, the block interleaver being configurable to interleave a block of encoded data, and wherein the interleaver configurations comprise a number of columns and a number of rows, the number of rows based on a number of coded bits per subcarrier per stream.
 27. The communication station of claim 26, wherein for a minimum bandwidth unit having 54 data subcarriers for 256-point FFT processing, the interleaver configuration has 9 columns and a number of rows equaling 3 times a number of coded bits per single subcarrier.
 28. The communication station of claim 26, wherein the communication station further comprises: an encoder to encode input data prior to interleaving in accordance with one of a plurality of code rates; and a constellation mapper to map the encoded data after the interleaving to a QAM constellation, wherein the encoder and mapper operate in accordance with one of a plurality of predetermined modulation and coding scheme (MCS) combinations for the subcarrier allocation, wherein the plurality of predetermined MCS combinations for the subcarrier allocation are restricted to an integer number of coded bits per OFDM symbol (Ncbps) and an integer number of data bits per OFDM symbol (Ndbps).
 29. The communication station of claim 21 wherein the longer-duration OFDM symbols are to be selected for larger delay spread environments, and wherein standard-duration OFDM symbols are to be selected for smaller delay-spread environments.
 30. The communication station of claim 29 wherein the standard-duration OFDM symbols have a symbol duration that ranges from 3.6 micro-seconds (us) including a 400 nanosecond (ns) short guard interval to 4 us including an 800 ns guard interval, and wherein the longer-duration OFDM symbols have a symbol duration is one of either 2× or 4× the duration of the standard-duration OFDM symbols.
 31. The communication station of claim 21 further comprising one or more processors and memory, and wherein the physical layer circuitry includes a transceiver.
 32. The communication station of claim 31 further comprising two antennas coupled to the transceiver.
 33. A method performed by a high-efficiency WLAN (HEW) communication station (STA) comprising: communicating longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configuring the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols, wherein the longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.
 34. The method of claim 33 further comprising processing the longer-duration OFDM symbols with a fast-Fourier Transform (FFT), wherein for processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit is to be of 48, 54 or 60 data subcarriers, and wherein for processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit is to be of 28 or 30 data subcarriers.
 35. The method of claim 34, wherein for processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 48, 50, 54, 52, 54, 56, 60 or 62 data subcarriers, and wherein for processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 24, 26, 28 or 30 data subcarriers.
 36. The method of claim 33 further comprising: selecting the longer-duration OFDM symbols for larger delay spread environments; and selecting the standard-duration OFDM symbols for smaller delay-spread environments.
 37. A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors to perform operations to configure a high-efficiency WLAN (HEW) communication station (STA) to: communicate longer-duration orthogonal frequency division multiplexed (OFDM) symbols on channel resources in accordance with an orthogonal frequency division multiple access (OFDMA) technique, the channel resources comprising one or more minimum bandwidth units, each minimum bandwidth unit having a predetermined number of data subcarriers; and configure the minimum bandwidth units in accordance with one of a plurality of subcarrier allocations for one of a plurality of interleaver configurations for communication of the longer-duration OFDM symbols; wherein the longer-duration OFDM symbols have symbol duration that is either 2× or 4× a standard OFDM symbol duration.
 38. The non-transitory computer-readable storage medium of claim 37, wherein the longer-duration OFDM symbols are processed with a fast-Fourier Transform (FFT), wherein for processing the longer-duration OFDM symbols with a 256-point FFT without code-rate exclusions, the predetermined number of data subcarriers for the minimum bandwidth unit is to be of 48, 54 or 60 data subcarriers, and wherein for processing the longer-duration OFDM symbols with a 128-point FFT without code-rate exclusions, the number of data subcarriers for the minimum bandwidth unit is to be of 28 or 30 data subcarriers.
 39. The non-transitory computer-readable storage medium of claim 38, wherein for processing the longer-duration OFDM symbols with the 256-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 48, 50, 54, 52, 54, 56, 60 or 62 data subcarriers, and wherein for processing the longer-duration OFDM symbols with the 128-point FFT with a code-rate exclusion of 5/6 for 256-QAM, the number of data subcarriers for the minimum bandwidth unit is to be of 24, 26, 28 or 30 data subcarriers.
 40. The non-transitory computer-readable storage medium of claim 37, wherein the longer-duration OFDM symbols are to be selected for larger delay spread environments, and the standard-duration OFDM symbols are to be selected for smaller delay-spread environments. 